What is software-defined networking (SDN)

Short answer

Software-defined networking (SDN) separates the network's control logic (control plane) from the actual packet forwarding (data plane). Instead of each router making independent decisions, a central controller programs all network devices. This makes networks programmable, agile, and easier to manage at scale. For related network configuration, see how to configure DNS records.

How it works

Traditional network: Each router runs its own routing protocol and makes forwarding decisions independently.

SDN: A central controller has a global view of the network and pushes forwarding rules to all switches. If a link fails, the controller recalculates paths and updates all switches instantly.

Three layers: 1. Application layer — Network apps (firewall, load balancer, monitoring) 2. Control layer — Central SDN controller (the "brain") 3. Infrastructure layer — Switches and routers (the "muscle")

Benefits

• Centralized management: Change once, apply everywhere
• Automation: Provision new networks in minutes, not weeks
• Programmability: APIs to create, modify, and delete network configurations
• Multi-tenancy: Isolate different departments or customers on shared infrastructure

Tips

• SDN is most valuable in large, dynamic environments (cloud providers, data centers)
• For smaller networks, traditional management with good VLAN design suffices — see how to configure VLANs
• OpenFlow is the original SDN protocol, but many vendors use proprietary alternatives today